The long-term goal of this application is to further the understanding of the role of inhibitory receptors in information processing. Information about odors is transduced into electrical impulses by olfactory receptor neurons (ORNs) and transmitted to the central nervous system for further processing. Recent studies indicate that in some species, the output of ORNs is modified by the activation of inhibitory receptors expressed in the afferent terminals of the receptor cells. Although the effect of the inhibition on receptor cell signaling is unclear, the activity of these receptors is likely to critically affect the synaptic strength of contacts between ORNs and their targets in the brain. This application seeks to investigate the molecular nature of these receptors in the olfactory system of the American lobster, Homarus americanus. In the lobster, presynaptic inhibition of ORNs is produced by ionotropic receptors that mediate the effects of gamma aminobutyric acid (GABA). One candidate subunit of this receptor is the recently isolated cDNA that encodes an ionotropic GABA receptor subunit (lob GABA 1). The preliminary data show that lob GABA 1 is highly expressed in lobster ORNs. Subunit specific antisera will be prepared and used in immunocytochemical studies to determine the location of expression of lob GABA 1. Additional subunits that comprise this receptor will also be isolated and the physiological and pharmacological properties of the co-assembled subunits will be examined. Understanding how inhibitory receptors function in sensory signaling is important to the overall understanding of how information is processed in the nervous system. The results of this study will establish the molecular identity of the presynaptic receptors inhibiting the output of ORNs in the olfactory system of the lobster and will provide the preliminary data that will be used to investigate the function of the receptors in the processing of odor signals.